FILE - In this June 20, 2017 file photo provided by South Korean Defense Ministry, U.S. Air Force B-1B bombers, top, and second from top, and South Korean fighter jets F-15K fly over the Korean Peninsula, South Korea. A South Korean lawmaker said Tuesday, Oct. 10, 2017, that North Korean hackers may have stolen highly classified military documents that include U.S.-South Korean wartime "decapitation strike" plans against the North, according to South Korean media reports. (South Korean Defense Ministry via AP, File)

SEOUL, South Korea (AP) — A South Korean lawmaker says North Korean hackers stole highly classified military documents that include U.S.-South Korean wartime “decapitation strike” plans against the North Korean leadership.

The United States, meanwhile, staged another show of force meant to deter any North Korean aggression by flying two B-1B supersonic bombers Tuesday night from an air base in the U.S. territory of Guam to the South for drills with South Korean jets. Such flights by the powerful aircraft based in Guam incense the North, which claims they are preparation for war; Pyongyang has threatened to send missiles into the waters around Guam.

If confirmed, the reported hacking attack by the North would be a major blow for South Korea at a time when its relations with rival North Korea are at a low point. The South has taken an increasingly aggressive stance toward the North’s belligerence amid back-and-forth threats of war between North Korea and U.S. President Donald Trump. North Korea’s possession of secret war plans would require a major overhaul of how South Korea and its ally Washington would respond if there’s another war on the Korean Peninsula.

An unusually aggressive approach to the North by Trump, which has included rhetoric hinting at U.S. strikes and threatening the destruction of North Korea’s leadership, has some South Koreans fearful that war is closer than at any time since the Korean War ended in 1953 in a shaky ceasefire, leaving the Korean Peninsula still technically in a state of war.

Rep. Lee Cheol-hee, a lawmaker for the ruling Democratic Party who sits on the National Defense Committee, said defense sources told him that North Korean hackers last year stole the classified U.S.-South Korean war plans, including parts of Operational Plan 5015, which includes procedures for a decapitation strike on the North’s leadership if a crisis breaks out or appears imminent.

The Defense Ministry after an investigation said in May that North Korea was likely behind the hacking of the Defense Integrated Data Center in September last year, but had refused to confirm media speculation that the decapitation strike plan was compromised. Defense officials refused to comment Wednesday.

Lee, who didn’t specify his sources, said the plans allegedly stolen by the North includes operations for tracking the movement of the North’s leadership, isolating their hideouts, executing air assaults and follow-up actions for securing and eliminating targets, which would obviously include North Korean leader Kim Jong Un.

A pre-emptive strike against Pyongyang’s leadership would be difficult to undertake, but it’s widely seen as the most realistic of the limited military options Seoul has to deny a nuclear attack from its rival.

Outside governments and international human rights organizations say Kim rules as a tyrant over a largely malnourished and abused population while enjoying a luxurious lifestyle backed up by a weapons program nearly advanced enough to viably target the U.S. mainland with nuclear-tipped missiles. But Kim, the third generation of his family to rule, is officially revered in the North, and any suggestion of removing him from power is taken extremely seriously in Pyongyang.

Lee said that 235 gigabytes of military documents were taken, but the ministry has yet to identify 80 percent of the documents that were compromised. Other stolen data included contingency plans for South Korean special forces and information on military facilities and power plants, he said.

Seoul says North Korea has repeatedly staged cyberattacks on South Korean business and government websites. North Korea routinely denies responsibility.

Not long after the news of the alleged cyberattacks broke, two B-1B bombers few from Guam to conduct drills with two South Korean fighter jets Tuesday night, a South Korean Defense Ministry official said, requesting anonymity because of department rules.

The U.S. bombers staged simulated air-to-ground missile striking drills off the peninsula’s east coast before flying across the country accompanied by the two South Korean jets. The aircraft then conducted similar simulated air to ground striking drills off the peninsula’s west coast, the official said.

North Korea has yet to comment on either the bombing drills or the hacking claims.